Most enterprise networks and corresponding data centers are deployed as multiple physical sites distributed in different geographical locations to improve reliability and provide redundancy. The physical sites are configured to provide similar services and are able to perform layer-2 communications with each other. In order to implement dynamic resource allocation and management across the sites, a virtual machine should be able to transit freely between the data centers. The transition of the virtual machine should be transparent to users which require the virtual machine to have a constant IP address, thus layer-2 networks of the sites located at different locations should be interconnected.
Ethernet virtual interconnect (EVI) is a technique providing Ethernet interconnections across sites via virtual links. Based on conventional service provider and enterprise networks, EVI provides flexible layer-2 interconnections for distributed physical sites.